Nobody commented, so I went ahead and deployed it. Let me know if you have thoughts now that it's been forced upon you. :)
Thought: it basically looks like the default thing where links that you've already clicked are a different colour.
Yeah, the goal was for it to feel pretty natural.
It so happens that, since i've read (or clicked on) all the LW posts, I (personally) end up seeing a sea of grey that feels a bit weird, but I think this is actually a pretty rare experience.
I actually didn't notice that it was a new feature. I had just assumed that visited links had always been gray.
Over on Lessestwrong.com (our sometimes-staging-site), we're trying out an update to how post items display on the frontpage. Posts that you've read now appear slightly grey. The goal is to make it so you can tell when you've read a post at a glance, without making it feel like unread posts are shouting at you to read them or feel like an obligation.
You can log in on lessestwrong using your usual login, and see how it feels.